An aircraft APU is usually run on the ground during passenger boarding and deplaning. The APU turns an electric generator that powers the electrical system when the main engines of an aircraft are off. It also provides pneumatic pressure for air conditioning and starting the main engines. An APU eliminates the need for using an external power source and a noisy air compressor cart to keep the cabin comfy while boarding.
An APU typically includes a jet turbine engine that drives an electrical generator and other equipment, an electronic control unit (ECU), and cockpit-mounted controls. The jet turbine engine of the APU includes one or more compressor stages that draw in and compress outside air. Some of the pressurized air may be diverted from the compressor via bleed air extraction, to supply one or more downstream air conditioning packs.
An air conditioning pack is an air cycle machine (ACM) that serves as a refrigeration unit of an environmental control system (ECS). Many aircraft have two or more air conditioning packs. The air cycle cooling process compresses, cools and expands air (instead of a phase changing refrigerant such as Freon) in the gas cycle. Cooled air output from the process is used directly for cabin ventilation.
Unfortunately, bleed air can be contaminated with various substances, including some arising from heated engine oils, hydraulic fluid and other vaporized contaminants. Consequently, cabin air can be contaminated by various substances that are drawn in through the APU and, via the engine bleed, enters the air-conditioning pack and passes into the aircraft cabin environment. Exposure to fumes and vapors can result in crew and passenger discomfort as well as acute, short-term respiratory problems, and even panic.
By maintaining a clean APU, such contamination may be substantially reduced. By way of example, an APU may be periodically steam-cleaned to remove accumulated contaminants. However, heretofore, such cleaning was performed infrequently because it was costly and time consuming.
Additionally, environmental sensitivities, rules and regulations prohibit wastewater from such a cleaning process to run off onto airport grounds. Such wastewater, which is considered industrial wastewater, should be recycled, reused or discharged for treatment to onsite airport treatment systems or to an offsite treatment facility.
A system and method for frequent rapid cleaning of aircraft APUs without runoff to the ground is needed. The system should be mobile and easy to deploy before a flight. The method should be efficient and reliable.
The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above.